1. Field of Invention
The invention relates to a parking apparatus of an automatic transmission.
2. Description of Related Art
Hitherto, a vehicle having an automatic transmission mounted thereon has a structure in which a torque generated by operating an engine is transmitted to the transmission through a torque converter. Then, the torque is converted by the transmission, and then the converted torque is transmitted to drive wheels. In this case, unlike the vehicle provided with a manual transmission, the vehicle cannot be kept stopped by the gear position (the gear ratio) selected to stop the vehicle and inertia of the engine.
Therefore, a method has been employed in which a parking pole is rotated in synchronization with the operation of a shift lever when the parking range has been selected by operating the shift lever. Thus, a claw provided for the parking pole and a tooth space of the parking gear connected to an output shaft of the automatic transmission are engaged to each other so that the output shaft is locked (refer to Japanese Patent Laid-Open No. 61-41622).
FIG. 1 is a front view showing a conventional parking apparatus of an automatic transmission. FIG. 2 is a side view showing the conventional parking apparatus of the automatic transmission.
Referring to FIGS. 1 and 2, the parking apparatus of the automatic transmission incorporates a rod 83 arranged to be moved forwards/reversely (from side to side in FIG. 2) by a detent lever (not shown); a cam 84 slidably disposed along the rod 83 at a predetermined position thereof so as to convert linear motion into rotational motion; a parking pole 87 having a claw 94 in the substantially central portion thereof and arranged to be swung when the cam 84 is moved forwards or reversely; and a parking gear 66. The leading end of the parking pole 87 is supported by the cam 84.
The parking gear 66 is connected to an output shaft (not shown) so that the parking gear 66 is rotated in a direction indicated by an arrow A when the vehicle is moved forwards. When the vehicle is moved in reverse, the parking gear 66 is rotated in a direction indicated by an arrow B. The parking pole 87 is supported swingably about the pole shaft 93. When the parking pole 87 is rotated in a direction indicated by an arrow C, the parking pole 87 causes the claw 94 and a tooth space 62 of the parking gear to be engaged to each other. When the parking pole 87 is rotated in a direction indicated by an arrow D, the claw 94 and the tooth space 62 are disengaged. The pole shaft 93 is provided with a torsion spring (not shown) so that the parking pole 87 is urged in the direction indicated by the arrow D.
The detent lever is connected to a manual shaft (not shown) arranged to be rotated in synchronization with the operation of a shift lever (not shown) disposed in a driver's seat. The detent lever formed as a plate-like member arranged to be rotated about the manual shaft has a plurality of engagement grooves corresponding to the shifting positions of the shift lever formed in the peripheral portion thereof. The leading end of a detent spring (not shown) can be engaged to any one of the engagement grooves. Therefore, when the shift lever is operated and thus the detent lever is rotated, the rod 83 is moved forwards or reversely to follow the rotation of the detent lever.
A compression spring 85 is provided for the rod 83 at a position to rearward (at a right-hand position in FIG. 2) of the cam 84. The cam 84 has a conical surface formed into two steps and having a vertex facing the front end of the rod 83.
When the rod 83 has been moved forwards (to the left in FIG. 2), the cam 84 is introduced into a position between a bracket 95 and the parking pole 87 so the parking pole 87 is moved upwards and rotated in the direction indicated by the arrow C. When the rod 83 has been moved reversely (to the right in FIG. 2), the cam 84 is separated from the position between the bracket 95 and the parking pole 87. Thus, the parking pole 87 is rotated in the direction indicated by the arrow D through the urging force of the torsion spring at the pole shaft 93.
When a vehicle which is being moved in a forward drive range or a reverse drive range is to be stopped and parked, the above-mentioned conventional parking apparatus of the automatic transmission requires a driver to depress a brake pedal (not shown) to stop the vehicle. Then, the driver operates the shift lever to select a parking range so that the output shaft is locked.
In the above-mentioned case, the accelerator pedal (not shown) has been released when the driver depresses the brake pedal to stop drive wheels (not shown). Therefore, an engine (not shown) is in an idling state. Since the engine and the drive wheels are connected to each other through a torque converter, a transmission and the like (not shown) in the above-mentioned idling state, the torque generated by the engine causes the drive wheels to be rotated. Therefore, the output shaft and the parking gear 66 are caused to be rotated in the direction indicated by the arrow A or B.
When the driver selects the parking range by operating the shift lever simultaneously with depression of the brake pedal to stop the vehicle, the claw 94 and the tooth space 62 are engaged with each other in a state in which the parking gear 66 would normally be rotated in the direction indicated by the arrow A or B, that is, in a state in which the drive force (the torque) is maintained.
In the foregoing case, the output shaft is undesirably locked in a state in which residual torque is retained between the parking gear 66 and the drive wheels. That is, a shaft provided for a power transmission system arranged from the output shaft to the drive wheels is brought to a state in which the shaft is twisted.
If the driver operates the shift lever to select another range in order to drive the vehicle, the residual torque between the parking gear 66 and the drive wheels is discharged rapidly. As a result, noise and shock are generated, thus making the driver feel uncomfortable.